The present invention relates to a solenoid driving apparatus for driving a solenoid that is used, for example, for various controls of automobiles.
As a solenoid driving apparatus for driving a solenoid, a constant-current driving circuit for inductive loads has been known, which has semiconductor integrated circuits for driving inductive loads, as disclosed in Japanese Patent Application Laid-Open No. 2001-117651.
FIG. 1 shows a typical circuit of a conventional solenoid driving apparatus. This solenoid driving apparatus includes a first current switching element 1, a second current switching element 2a, a third current switching element 3, a battery E, a solenoid L, a resistor R, zener diodes ZD1 and ZD2, a diode D4, an inverter 4, and a control circuit 5.
The first current switching element 1 has a transistor Q1 in the form of an N-channel MOSFET, and a diode D1 connected between the source and drain of the transistor Q1. The second current switching element 2a has a transistor Q2 in the form of an N-channel MOSFET, and a diode D2 connected between the source and drain of the transistor Q2. The third current switching element 3 has a transistor Q3 in the form of an N-channel MOSFET, and a diode D3 connected between the source and drain of the transistor Q3. Each of these diodes D1 to D3 is a parasitic diode.
The drain of the transistor Q1 is connected to the positive terminal of the battery E, and the negative terminal of the battery E is grounded. The source of the transistor Q1 is connected to the source of the transistor Q2, and the gate of the transistor Q1 is connected to the control circuit 5. The drain of the transistor Q2 is connected to the drain of the transistor Q3, and the gate of the transistor Q2 is connected to the control circuit 5. The source of the transistor Q3 is grounded, and the gate of the transistor Q3 is connected to the output end of the inverter 4. The input end of the inverter 4 is connected to the control circuit 5 and the gate of the transistor Q1.
One end of the solenoid L is connected to a junction A of the source of the transistor Q1 and the source of the transistor Q2, and the other end of the solenoid L is grounded. A resistor R is connected between the gate and source of the transistor Q2. The gate of the transistor Q2 is grounded through a series connection of a zener diode ZD1, a zener diode ZD2, and a diode D4.
In the solenoid driving apparatus, when an exciting current is supplied from the battery E to the solenoid L, a control signal S1 is fed from the control circuit 5, and in response thereto, the first current switching element 1 is brought into a conductive state and the third current switching element 3 is brought into a non-conductive state. As a result, the flow of the exciting current into the second and the third current switching elements 2a and 3 is blocked, and the exciting current is supplied to the solenoid L.
On the other hand, when the supply of the exciting current to the solenoid L is suspended, the first current switching element 1 is brought into a non-conductive state and the third current switching element 3 is brought into a conductive state in response to the control signal S1, and at the same time, the second current switching element 2a is brought into a conductive state in response to a control signal S2 fed from the control circuit 5.
As results, a loop current caused by the energy stored in the solenoid L passes through the second and the third switching elements 2a and 3. In this manner, the supply of the exciting current and the suspension thereof are made repetitively by using the control signals S1 and S2 according to PWM control, thereby achieving a constant-current control for the solenoid L.
When the constant-current control for the solenoid L is terminated, the first and the second current switching elements 1 and 2a are brought into a non-conductive state and the third current switching element 3 is brought into a conductive state in response to the control signals Si and S2. Consequently, in the second current switching element 2a, a constant-voltage operation is made by the zener diodes ZD1 and ZD2 as well as the diode D4. These are connected in series between the gate of the transistor Q2 and the ground. The energy stored in the solenoid L is released in a short time by this constant-voltage operation.